Referring to FIG. 5, a conventional rotary cam has a rotating unit 60 having a plurality of passive wheels 61 located at an outer edge thereof. The passive wheels 61 are disposed radially with equal spaces in between. The rotating unit 60 is corresponding with a cam 70, both of which are disposed in a base 80. When the rotating unit 60 rotates, the passive wheels 61 is restricted and driven by the cam 70 to further drive the rotating unit 60 with the cam 70. However, the conventional rotary cam may be disadvantageous because the design of using single motor to drive a single rotating unit 60, which cannot meet the requirement of mass production. If using multiple rotary cam equipment, more spaces will be occupied and it may need to hire more operators. Furthermore, the precision of the gear engagement is very important for the rotary cam equipment. Therefore, there remains a need for a new and improved rotary cam structure with seamless transmission to overcome the problems stated above.